BACKGROUND: To reduce production of resistant bacteria by over-use of antibiotics, an antibiotics restriction policy became effective in several hospitals. However, there are different views on its effect. This study aims to examine antibiotic resistance of pathogenic organisms cultured in tracheal aspirates of the patients who need to maintain mechanical ventilation in medical intensive care unit before and after the antibiotics restriction policy. METHODS: Before and after 2 years from August 2003, when carried out the antibiotics restriction policy in Gyeongsang university hospital, it was retrospectively investigated the antibiotic resistance pattern of bacteria cultured in tracheal aspirates of the patient who is maintained by mechanical ventilation more than 48 hours in the medical intensive care unit. Restricted antibiotics are ceftazidime, piperacillin/tazobactam, imipenem, meropenem, vancomycin, and teicoplanin. RESULTS: Before the antibiotics restriction policy, (Sep 2001~Aug 2003) and after, (Sep 2003~Aug 2005), there were 306 and 565 patients applied in each case and the total use of antibiotics, except piperacillin/tazobactam, was reduced and that of cefotaxime and ceftriaxone was increased. There was no significant change in antibiotic resistance among Acinetobacter, Pseudomonas, and Enterobacter species. CONCLUSION: The result of this study shows that the antibiotics restriction policy does not reduce production of antibiotic resistant bacteria in tracheal aspirate in a medical intensive care unit. However, it is considered that long-term observation may be necessary.